A lot of DJs who use laptops seem to suffer a depreciation in sound quality; I'm not saying it has to occur, but it often does.
i would guess the reason is just that laptops have opened up the prospect of Djing to a lot more people many of whom may not necessarily understand a whole lot about the principles of DJ ing ,accoustics or technical side of it
then there is the "why should i pay a DJ when i can do it myself" customer. hehe can you believe i met some salsa organizers who actually attempted to hold a salsa event with a hifi system once. lol
and the added factor of that any file can be played on a laptop no matter how dubious its origin.
but thats not to say that CD or vinyl DJs come with a guarantee that they know what they are doing.
its just a more expensive "club" to be a member of.
and personally i think pioneer CDjs are extortionate for what they do.
a laptop DJ who know what they are at will sound exactly as good as any other IMO
there is no software that i know of that is particularly salsa orientated but i like virtual DJ it does the job
and i would recommend to buy a sound card such as hercules Trim or hercules RMX (the controller version) mainly because those are the ones i use.
but they are a solid option. they will come with a free version of virtual DJ too. this is enough to get you on the way.
i totally agree with mambo T that its worth it to spend money on good speakers if your budget can do that
i got a set of RCF Art 312A speakers and just love them. would recommend those.